A helper method to the get the next property in the given String str with
a valid property substitution. A valid property looks like
#{jobParameter['batch.property']}. This method will return only the name
of the property found without the surrounding metadata.
Example:

Parameters:

str
The string to search.

startIndex
The index in str to start the search.

Returns:

The name of the next property found without the starting
#{<propertyType>[' or ending ']}